1. Field of the Invention
The present invention relates to a novel means and method of locking a screw member in position to a roof rafter or truss and there adapted to hold a roof covering therebetween. The screw threads are prevented from unfastening from the action of movement of the held down covering caused by wind action. In particular the invention provides the screw member with a ratched-toothed lock nut that will interlock with the ratchet teeth of a plate that is fixed to the roof and the roof covering thereby preventing unthreading of the screw when wind action causes the covering to lift and flap.
2. Description of the Prior Art
It is known to cover flat roofs with layers of tar and roofing paper and then cover the whole combination with gravel or crushed stone to ballast the covering from shifting and lifting from the action of the wind. During installation the tar has an offensive odor and the stone objectionalbe to handle and when the covering is removed an undesirable mess is caused. There is a need for a better means of covering a roof. As a response to the need roofers have turned to heavy sheets of elastomeric material such as rubber for use as roof covering. The sheets are overlapped and glued together along their mating edges with screw members fixing the sheets to the roof rafters or trusses of the roof. No stone ballast is required to hold down the rubber but when the pressure of a wind causes the covering to tend to lift the screws will unthread and loosen. There has been found that with this new type of roof covering a better means for securing the covering in place has been required.